A valve which permits gases (or fluids) to flow in one direction, and which automatically (without outside intervention) prevents gases from flowing in an opposite direction is commonly referred to as a "check valve", or a "one-way check valve". A typical check valve comprises a typically cylindrical valve body (chamber, housing) disposed between an inlet port and an outlet port. The inlet port communicates with an inlet orifice in the valve body, and may be integral with same. The outlet port communicates with an outlet orifice in the valve body, and may be integral with same. A movable member disposed within the valve body, such as a poppet (e.g., a disc), is biased (seated), typically by a spring which is also disposed within the valve body, against the inlet orifice so as to block gas from passing from the outlet orifice to the inlet orifice. When gas entering the inlet port exceeds a threshold predetermined "cracking" pressure (more accurately, a threshold positive pressure differential pressure between the inlet port and the outlet port), the movable member is urged by the differential gas pressure away from the inlet orifice, thereby permitting the gas to flow through the valve body, into the outlet orifice, and out of the outlet port. When the situation is reversed, and there is more pressure at the outlet port than at the inlet port, the movable member remains seated (in some instances, more securely) against the inlet orifice, preventing gas flow through the valve body. A resilient sealing member, such as an O-ring may also be used to ensure a gas-tight seal between the movable member and the inlet orifice.
The following references discuss check valves, generally:
U.S. Pat. No. 2,608,376 ("'376") discloses a construction of a check valve wherein a cylindrical member (e.g., 27) is moveable in a chamber (e.g., 26) and is normally biased by a coil spring (e.g., 37) to seal against a shoulder between a larger portion of the bore (e.g., 23; in the terms of the present patent application, the "valve body" or "housing") and a smaller portion thereof (in the terms of the present patent application, the "inlet orifice").
The coil spring of the '376 patent is disposed within the valve body, and is therefore (i) subjected to the fluids (e.g., gases) flowing through the check valve and (ii) inaccessible for adjusting the threshold opening force (also known as "cracking pressure").
It bears mention here that any internal moving part of a check valve has the potential to, and often does, add particulate matter to the fluid flow. This is particularly true in the case of springs which shed particles, albeit microscopic particles, as they flex back and forth. Such contaminants are undesirable in high-purity applications such as semiconductor manufacture. Another problem inherent in check valve design is elastomer sealing members which can be "wetted" by the fluid flow, making it difficult to completely purge the system of residual fluids (contaminants). Evidently, the larger the surface area of the elastomer sealing member exposed to fluid flow, the more wetting (residual surface contamination) will occur.
Another problem inherent with conventional check valves is that there is no facile means for eliminating the biasing force to allow for bi-directional flow. This problem is addressed by and solved by the present invention.
It is known to use magnets, either alone or in combination with the aforementioned springs, as biasing components to exert a closing force on the poppet (moving member) of a one-way check valve. The following references disclose the use of magnets:
U.S. Pat. No. 2,646,071 ("'071") discloses a magnetic check valve which includes a valve disc (e.g., 35; in the terms of the present patent application, a "poppet") and a magnet (e.g., 26) disposed within the chamber (28; in the terms of the present patent application, the "inlet orifice"). In one disclosed embodiment, the valve disc (40) is non-magnetic, and includes a magnetic member (42) which is disposed so as not to align with the valve seat (25). As aptly noted in this patent, when employing a valve disc which possesses magnetic properties, it is important to avoid the problem of ferrous metal particles being attracted to the disc in a location which would prevent a tight closure between said disc (poppet) and said valve seat (inlet orifice).
The magnet(s) of the '071 patent are disposed within the valve body, and are therefore (i) subjected to the fluids (e.g., gases) flowing through the check valve and (ii) inaccessible for adjusting (or eliminating) the threshold opening force.
U.S. Pat. No. 2,667,895 ("'895") discloses a magnetically biased check valve wherein the poppet (valve 20) is a cylindrically-shaped magnet which is free to move within the valve body, toward and away from the valve seat (18). The valve body components (housing 10 and bonnet 12) are of a non-magnetic material (brass). A second cylindrical magnet 26 is fixed immovably within the valve body in orientation wherein it will exert a closing force on the magnet-poppet.
The magnet(s) of the '895 patent are disposed within the valve body, and are therefore (i) subjected to the fluids (e.g., gases) flowing through the check valve and (ii) inaccessible for adjusting the threshold opening force.
U.S. Pat. No. 2,949,931 ("'931") discloses a magnetic check valve having an annular tubular permanent magnet 21 disposed within the valve body. In this example, the poppet is a disc 28 which is made from any suitable permeable material such as iron and the like, and the poppet 28 is biased against the inlet orifice by the magnet 21.
None of the above-referenced check valves are "bi-directional", capable of flowing fluids in two opposite directions.
In certain fluid-flow applications, such as the high-purity applications associated with semiconductor manufacturing, it is often necessary to evacuate a system (e.g., a piping system) which has been filled with hazardous (e.g., toxic, caustic) gases via a check valve. In order to evacuate the system, a vacuum pump is connected to the downstream side of the check valve. When pulling a vacuum, the pressure differential decreases until it is less than the cracking pressure. Once this occurs, it is inherent that the poppet shuts and isolates the upstream side, prior to achieving the vacuum maintained on the downstream side. This results in there being residual fluids within the system on the upstream side of the check valve.
Additional references of interest are: U.S. Pat. No. 3,217,736, U.S. Pat. No. 3,076,417, U.S. Pat. No. 4,275,759, U.S. Pat. No. 4,489,754, U.S. Pat. No. 5,320,136 and German Patent No. 212,570.